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Foellmi, Karl

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Foellmi, Karl
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https://libra.unine.ch/handle/123456789/140

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  • Publication
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    Soil phosphorus uptake by continuously cropped Lupinus albus: A new microcosm design
    (2006-12-12)
    Le Bayon, Renée-Claire 
    ;
    Weisskopf, Laure
    ;
    Martinoia, Enrico
    ;
    Jansa, J
    ;
    Frossard, Emmanue
    ;
    Keller, F
    ;
    Foellmi, Karl 
    ;
    Gobat, Jean-Michel 
    When grown in soils with sparingly available phosphorus (P), white lupin (Lupinus albus L.) forms special root structures, called cluster roots, which secrete large amounts of organic acids and concomitantly acidify the rhizosphere. Many studies dealing with the understanding of this P acquisition strategy have been performed in short time experiments either in hydroponic cultures or in small microcosm designs with sand or sand:soil mixtures. In the present study, we applied an experimental design which came nearer to the natural field conditions: we performed a one-year experiment on large microcosms containing 7 kg of soil and allowing separation of rhizosphere soil and bulk soil. We planted six successive generations of lupins and analysed P uptake, organic P desorption, phosphatase activities and organic acid concentrations in different soil samples along a spatio-temporal gradient. We compared the rhizosphere soil samples of cluster (RSC) and non-cluster roots (RSNC) as well as the bulk soil (BS) samples. A total shoot biomass of 55.69 +/- 1.51 g (d.w.) y(-1) was produced and P uptake reached 220.59 +/- 5.99 mg y(-1). More P was desorbed from RSC than from RSNC or BS (P < 0.05). RSC and RSNC showed a higher activity of acid and alkaline phosphatases than BS samples and a higher acid phosphatase activity was observed in RSC than in RSNC throughout the one-year experiment. Fumarate was the most abundant organic acid in all rhizosphere soil samples. Citrate was only present in detectable amounts in RSC while malate and fumarate were recovered from both RSC and RSNC. Almost no organic acids could be detected in the BS samples. Our results demonstrated that over a one-year cultivation period in the absence of an external P supply, white lupin was able to acquire phosphate from the soil and that the processes leading to this P uptake took place preferentially in the rhizosphere of cluster roots.
  • Publication
    Métadonnées seulement
    Carbonaceous and phosphate-rich sediments of the Miocene Monterey Formation at El Capitan State Beach, California, USA
    (2002)
    John, Cédric M
    ;
    Foellmi, Karl 
    ;
    De Kaenel, Eric
    ;
    Adatte, Thierry 
    ;
    Steinmann, Philipp
    ;
    Badertscher, Christophe
    The organic- and phosphate-rich interval of the Monterey Formation at El Capitan State Beach (west of Santa Barbara, California, U.S.A.; late early to early late Miocene in age) is composed of a carbonaceous marl (TOC contents between 1.2 and 23.2 wt %) with intercalated phosphate-rich laminae, lenses, and layers. Subordinate lithologies include ash layers, dolomitized horizons, and siliceous beds. We distinguished five lithological units: (1) a gray marl unit lacking major phosphate accumulations (> 16.3 Ma; average TOC content 2% by weight; average sedimentation rate 75 m/My; average TOC accumulation rate 0.19 mg/cm(2)/yr); (2) a black marl unit including light-colored phosphatic laminae, lenses, and discrete particles (16.3-14.5 Ma; average TOC content 7.5% by weight; average sedimentation rate 20 m/My; average TOC accumulation rate 0.19 mg/cm(2)/yr); (3) a red marl unit including light-colored phosphatic laminae, lenses, and commonly reworked particles (14.5-12.7 Ma; average TOC content 15% by weight; average sedimentation rate 20 m/My (14.5-13.3 Ma) and 2 m/My (13.3-12.7 Ma), respectively; average TOC accumulation rate 0.39 mg/cm(2)/yr (14.5-13.3 Ma) and 0.04 mg/cm(2)/yr (13.3-12.7 Ma), respectively); (4) a unit of complex and condensed phosphatic beds, interbedded with red marl (12.7-10.8 Ma; average sedimentation rate 3 m/My); and (5) a black marl unit with intercalated phosphatic laminae and lenses (< 10.8 Ma; average sedimentation rate 9 m/My; average TOC accumulation rate 0.09 mg/cm(2)/yr). Phosphogenesis and accumulation of phosphate were dynamic processes, which started with local phosphogenesis leading to the formation of phosphatized particles, as well as stratigraphically bound phosphogenesis leading to the formation of phosphate laminae and lenses. Phases of subsequent sediment reworking resulted in the concentration of phosphate particles in phosphate-rich layers, and repeated phases of sediment reworking and phosphogenesis ultimately resulted in the formation of the complex phosphate condensed horizons. Preservation of organic matter was favored by high productivity rates and by the development of dysaerobic bottom-water conditions. The dynamic sedimentary environment likely led to the formation of early diagenetic phosphatic lids (which may have sealed off subjacent organic-rich layers) as well as to the rapid deposition of entire layers in the form of mud flows, thereby eventually enhancing the potential of organic-matter preservation. Our new age data suggest that at the El Capitan State Beach section the intervals characterized by high TOC values and maximum TOC accumulation rates (red marl), as well as significant quantities of in situ phosphates appeared in the late middle Miocene, i.e., during and after the major cooling phase at around 14.5 Ma. This implies that deposition of phosphate and organic carbon continued well after this cooling phase, thereby underlining the observation that preservation of organic carbon in the Monterey Formation is not only dependent on climate change during the mid Miocene but also on regional conditions.
  • Publication
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    Paleoceanographic changes during the early Cretaceous (Valanginian-Hauterivian): evidence from oxygen and carbon stable isotopes
    (2000)
    Van De Schootbrugge, Bas
    ;
    Foellmi, Karl 
    ;
    Bulot, Luc G
    ;
    Burns, Stephen J
    We investigated Valanginian-Hauterivian bulk rock and belemnite samples from Vocontian Basin sections in southeastern France for their stable carbon and oxygen isotope signature. Firstly, because these sections permit calibration with high-resolution biostratigraphy based on ammonites and secondly because detailed isotope studies for the Hauterivian are lacking. The results show that delta(13)C values for bulk rock decrease during the late Valanginian-early Hauterivian with 1 parts per thousand and increase again during the late Hauterivian with 1 parts per thousand. The delta(18)O signal for bulk rock samples is mostly disturbed by diagenesis, The belemnites show carbon and oxygen isotope values that are lower and higher than bulk rock samples respectively. We explain this as the result of the belemnites recording a deeper water signal with lighter delta(13)C values and heavier delta(18)O values, implicating colder water at greater depth. The overall preservation of the belemnites is very good and permits the construction of a paleo-temperature trend. This trend shows warm deeper water temperatures during the late early Valanginian (15 degrees C) and progressively cooler temperatures during the late Valanginian and early Hauterivian (11 degrees C), During the late Hauterivian temperatures increase again (13 degrees C). We relate this cooling trend for deeper water to a second order sea level rise, which allowed for the exchange of cold Boreal and warm Tethyan water masses. The influx of cold nutrient rich water had a profound effect on carbonate producing biota along the northern margin of the Tethys during the Hauterivian leading to prolonged phases of condensation and platform destruction. During the early Hauterivian the carbonate system along the northern Tethyan margin shifted into a 'green water' mode of carbonate production. High rates of carbonate production under mesotrophic conditions, also observed in other parts of the world, meant that the global carbon cycle became buffered shown by the stable trends in carbon isotopes. (C) 2000 Elsevier Science B.V. All rights reserved.
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